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Surface tension of liquid metal： role, mechanism and application

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Frontiers in Energy 2017年第4期11卷 535-567页

作者： Xi ZHAO Shuo XU Jing LIU Beijing Key lab of CryoBiomedical Engineering and Key lab of Cryogenics Technical Institute of Physics and Chemistry Chinese Academy of Sciences Beijing 100190 China Beijing Key lab of CryoBiomedical Engineering and Key lab of Cryogenics Technical Institute of Physics and Chemistry Chinese Academy of Sciences Department of Biomedical Engineering School of Medicine Tsinghua University Beijing 100084 China

Surface tension plays a core role in dominating various surface and interface phenomena. For liquid metals with high melting temperature, a profound understanding of the behaviors of surface tension is crucial in industrial processes such as casting, welding, and solidification, etc. Recently, the room temperature liquid metal （RTLM） mainly composed of gallium-based alloys has caused widespread concerns due to its increasingly realized unique virtues. The surface properties of such materials are rather vital in nearly all applications involved from chip cooling, thermal energy harvesting, hydrogen generation, shape changeable soft machines, printed electronics to 3D fabrication, etc. owing to its pretty large surface tension of approximately 700 mN/m. In order to promote the research of surface tension of RTLM, this paper is dedicated to present an overview on the roles and mechanisms of surface tension of liquid metal and summarize the latest progresses on the understanding of the basic knowledge, theories, influencing factors and experimental measure- ment methods clarified so far. As a practical technique to regulate the surface tension of RTLM, the fimdamental principles and applications of electrowetting are also interpreted. Moreover, the unique phenomena of RTLM surface tension issues such as surface tension driven self- actuation, modified wettability on various substrates and the functions of oxides are discussed to give an insight into the acting mechanism of surface tension. Furthermore, future directions worthy of pursuing are pointed out.

关键词： surface tension liquid metal soft machine,printed electronics electrowetting self-actuation

Rotor orientation direction controls geometric curvature and chirality for assemblies of motor amphiphiles in water

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Aggregate

Aggregate 2023年第2期4卷 237-246页

作者： Yun-Han Yang Yang Qin Yang Zhang Ling Zhang PCFM lab and GDHPRC lab School of ChemistrySun Yat-Sen UniversityGuangzhouChina

Control over geometric curvature and chirality of assemblies in pure aqueous media is key to the design of responsive materials and molecular *** we show how aggregate geometric curvature and chirality of motor amphiphiles could be switched from bicontinuous calabashes to nanoribbons or from vesicles to nanoribbons by modulating rotor orientation direction with dual light/heat stimuli to influence spontaneous curvature in *** photoisomerization and thermal helix inversion processes of molecular motors have been studied at the molecular level,and the transformation of supramolecular assemblies has been investigated at the microscopic *** morphological evolution of the calabash-shaped assembly can be kinetically captured,suggesting that the bicontinuous calabash-shaped structures are different from the bowl-shaped aggregates based on solvent-driven assembly upon the addition of non-solvent or *** investigation of dual optical/thermal control of rotor orientation can provide a new strategy for tuning the geometric curvature and chirality of nanoassemblies at the nanoscale,arriving ultimately the clusteroluminescence through-space electronic communication at responsive supramolecular nanosystems.

关键词： aqueous media chiral control curvature control dynamic assemblies molecular motor rotor orientation direction

Numerical Simulation and Analysis of Solid-liquid Two-phase Flow in Centrifugal Pump

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Chinese Journal of Mechanical Engineering 2013年第1期26卷 53-60页

作者： ZHANG Yuliang LI Yi CUI Baoling ZHU Zuchao DOU Huashu The State Key lab of Fluid Power Transmission and Control Zhejiang University The Province Key lab of Fluid Transmission Technology Zhejiang Sci-Tech University

The flow with solid-liquid two-phase media inside centrifugal pumps is very complicated and the relevant method for the hydraulic design is still immature so far. There exist two main problems in the operation of the two-phase flow pumps, i.e., low overall efficiency and severe abrasion. In this study, the three-dimensional, steady, incompressible, and turbulent solid-liquid two-phase flows in a low-specific-speed centrifugal pump are numerically simulated and analyzed by using a computational fluid dynamics （CFD） code based on the mixture model of the two-phase flow and the RNG k-~ two-equation turbulence model, in which the influences of rotation and curvature are fully taken into account. The coupling between impeller and volute is implemented by means of the frozen rotor method. The simulation results predicted indicate that the solid phase properties in two-phase flow, especially the concentration, the particle diameter and the density, have strong effects on the hydraulic performance of the pump. Both the pump head and the efficiency are reduced with increasing particle diameter or concentration. However, the effect of particle density on the performance is relatively minor. An obvious jet-wake flow structure is presented near the volute tongue and becomes more remarkable with increasing solid phase concentration. The suction side of the blade is subject to much more severe abrasion than the pressure side. The obtained results preliminarily reveal the characteristics of solid-liquid two-phase flow in the centrifugal pump, and are helpful for improvement and empirical correction in the hydraulic design of centrifugal pumps.

关键词： centrifugal pump solid-liquid two-phase particle property hydraulic performance abrasion numerical simulation

Swell induced stress in a hydrogel coating

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Acta Mechanica Sinica 2021年第5期37卷 797-802,I0002页

作者： Shuyang Wang Zhengjin Wang Yan Yang Tongqing Lu State Key lab for Strength and Vibration of Mechanical Structures Soft Machines LabSchool of Aerospace EngineeringXi’an Jiaotong UniversityXi’an 710049China

A hydrogel can be coated on various substrates to enable multiple *** applications include biomedical devices,anti-fouling surfaces and *** practical use,hydrogel coatings are often submerged in *** swell of hydrogel coating deteriorates the interfacial bonding with the *** paper presents a stress analysis of a hydrogel coating on a cylindrical metal *** adopt the thermodynamic theory coupling large deformation and water migration and formulate two boundary value problems for the coating-substrate system with and without an interfacial *** inhomogeneous stress fields in the hydrogel coating are *** influences of modulus,thickness of the hydrogel coating on the maximum radial stress at the interface are *** results may guide the design of hydrogel coating to avoid interfacial failure.

关键词： Hydrogel coating Swell Interfacial crack Boundary value problem

Solving the initial condition of the string relaxation equation of the string model for glass transition:part-I

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Chinese Physics B 2010年第5期19卷 450-459页

作者：张晋鲁王丽娜周恒为张丽丽赵兴宇黄以能 Department of Physics and National lab of Solid State Microstructures Nanjing University Xinjiang lab of Phase-transitions and Microstructures of Condensed Matters Yili Normal University

The string model for the glass transition can quantitatively describe the universal a-relaxation in glassformers, including the average relaxation time, the distribution function of the relaxation time, and the relaxation strength as functions of temperature. The string relaxation equation （SRE） of the model, at high enough temperatures, simplifies to the well-known single particle mean-field Debye relaxation equation, and at low enough temperatures to the well-known Rouse-Zimm relaxation equation that describes the relaxation dynamics of linear macromolecules. However, its initial condition, necessary to the further model predictions of glassy dynamics, has not been solved. In this paper, the special initial condition （SIC） of the SRE, i.e. for straight strings and the dielectric spectrum technique that is one of the most common methods to measure the glassy dynamics, was solved exactly. It should be expected that the obtained SIC would benefit the solution of the general initial condition of the SRE of the string model, i.e. for stochastically spatially eonfigurating strings, as will be described in separate publications.

关键词： glass transition relaxation phenomenon dielectric relaxation

Experimental Study on a Centrifugal Pump with an Open Impeller during Startup Period

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Journal of Thermal Science 2013年第1期22卷 1-6页

作者： Yuliang Zhang Zuchao Zhu Yingzi Jin Baoling Cui Yi Li Huashu Dou The State Key lab of Fluid Power Transmission and Control Zhejiang University The Province Key lab of Fluid Transmission Technology Zhejiang Sci-Tech University

Transient performance of fluid machinery during transient operating periods, such as startup and stopping, has been drawn more attentions recently due to the growing engineering needs. In this paper, the transient behavior of a prototype centrifugal pump with an open impeller during rapid startup period is studied experimentally. The variations of the rotational speed, flow rate, head, and shaft power during rapid startup period are recorded in ex- periments at different discharge valve openings. In addition, the non-dimensional flow rate and head are also used to analyze the transient behavior. The research result shows that the rise characteristic of the rotational speed is not basically changed by working points, while mainly depends on the startnp characteristics of the driving motor. Compared with the rapid rise of the rotational speed, the flow rate rises slowly in the initial stage of startup. Moreover, the flow rate lags behind the rotational speed to rise to final stable value, and the delay becomes more severe with the increase of the discharge valve opening. The shaft power impact phenomenon generally exists in the process of startup. The non-dimensional analysis shows that the non-dimensional head is very high at the very beginning of startup, and quickly falls to the minimum, then gradually rises to final stable value, while the non-dimensional flow rate always shows the rise tendency during whole startup period. In conclusion, it is found from the non-dimensional results that the quasi-steady analysis is unable to accurately assess the transient flow during startup period.

关键词： centrifugal pump open impeller startup experimental study transient behavior

Pores-Preserving Face Cleaning Based on Improved Empirical Mode Decomposition

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Journal of Computer Science & Technology 2009年第3期24卷 557-567页

作者：刘艳丽徐晓刚郭延文王进段鑫陈曦彭群生 State Key lab of CAD & CG Zhejiang University Department of Mathematics Zhejiang University State Key lab of Novel Software Technology Nanjing University

In this paper, we propose a novel method of cleaning up facial imperfections such as bumps and blemishes that may detract from a pleasing digital portrait. Contrasting with traditional methods which tend to blur facial details, our method fully retains fine scale skin textures （pores etc.） of the subject. Our key idea is to find a quantity, namely normalized local energy, to capture different characteristics of fine scale details and distractions, based on empirical mode decomposition, and then build a quantitative measurement of facial skin appearance which characterizes both imperfections and facial details in a unified framework. Finally, we use the quantitative measurement as a guide to enhance facial skin. We also introduce a few high-level, intuitive parameters for controlling the amount of enhancement. In addition, an adaptive local mean and neighborhood limited empirical mode decomposition algorithm is also developed to improve in two respects the performance of empirical mode decomposition. It can effectively avoid the gray spots effect commonly associated with traditional empirical mode decomposition when dealing with high-nonstationary images.

关键词： image enhancement empirical mode decomposition normalized local energy

Big Learning with Bayesian methods

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National Science Review 2017年第4期4卷 627-651页

作者： Jun Zhu Jianfei Chen Wenbo Hu Bo Zhang TNList lab State Key Lab for Intelligent Technology and Systems CBICR Center Department of Computer Science and Technology Tsinghua University

The explosive growth in data volume and the availability of cheap computing resources have sparked increasing interest in Big learning, an emerging subfield that studies scalable machine learning algorithms,systems and applications with Big Data. Bayesian methods represent one important class of statistical methods for machine learning, with substantial recent developments on adaptive, flexible and scalable Bayesian learning. This article provides a survey of the recent advances in Big learning with Bayesian methods, termed Big Bayesian Learning, including non-parametric Bayesian methods for adaptively inferring model complexity, regularized Bayesian inference for improving the flexibility via posterior regularization, and scalable algorithms and systems based on stochastic subsampling and distributed computing for dealing with large-scale applications. We also provide various new perspectives on the large-scale Bayesian modeling and inference.

关键词： Big Bayesian Learning Bayesian non-parametrics regularized Bayesian inference scalable algorithms

Approximating the CIECAM02 color appearance model by means of neural networks

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Chinese Optics Letters 2004年第11期2卷 637-639页

作者：柴冰华廖宁放赵达尊 National lab of Color Science and Engineering

An artificial neural network used to realize the approximating problem of the color appearance model (CAM) CIECAM02 in color management is demonstrated. GretagMacbeth ColorChecker Charts, which now axe widely used in calibration of digital camera, are chosen as samples to implement the forward and reverse color appearance models. When the predictive results are evaluated, for forward model, the output color appearance space is converted to the uniform color space based on CAM and is evaluated, while for reverse model, because the prediction precision is insufficient, we try to convert the color appearance space, which is the cylinder space, to the cube space similar to the red, green, and blue (RGB) space, and the results show that the precision is obviously improved.

关键词： Color computer graphics Colorimetry Mathematical models Neural networks